1. Field of the Invention
The present invention relates to a variable resistor and, more particularly, to a residue-proof (e.g., dust-proof) variable resistor equipped with a case. The invention also pertains to a method for producing such a variable resistor.
2. Description of the Related Art
FIG. 36 shows a conventional variable resistor. The variable resistor 180 comprises an alumina substrate 184 having on its surface a horseshoe resistor 181, collector electrode thin film 183 and electrode thin films 182 respectively connected to end portions of the horseshoe resistor 181. A case 185 is provided for accommodating the alumina substrate 184 therein. Three lead terminals 186 (one of which is shown in FIG. 36) are allowed to pass through the alumina substrate 184 and are respectively soldered to the electrode thin films 182 and 183. A rotor 187 is accommodated in the case 185. A slider 189 is disposed on a rear surface of the rotor 187. A sealine O-ring 190 is disposed on the rotor 187 and a resin 191 is provided for sealing an opening in the rear surface of the case 185. Furthermore, when this variable resistor 180 is configured into a so-called xe2x80x9cside surface adjusting type variable resistorxe2x80x9d, wherein the resistance value is adjusted by rotating the rotor 187 from an arrow-indicated direction illustrated in FIG. 36, the lead terminals 186 are bent along the rear surface of the case 185.
An explanation will be given of the terminal numbers 1, 2 and 3 illustrated in FIG. 37 with reference to FIG. 38. It is now assumed that the lead terminal number 2 is the terminal connected to the slider 189 brought into sliding contact with the resistor 181. Next, it is assumed that the lead terminal number 3 is the terminal electrically connected to the end portion side of the resistor 181 on a side such that when the rotor 187 is rotated to the right the resistance value between this lead terminal and the lead terminal corresponding to the terminal number 2 becomes smaller. Finally, the lead terminal number 1 is the terminal electrically connected to the other end portion side of the resistor 181 on a side such that when the rotor 187 is rotated to the right the resistance value between this lead terminal and the lead terminal corresponding to the terminal number 2 becomes larger.
In the variable resistor 180 of the side surface adjusting type, various combinations are made among the resistance value adjusting direction, lead terminal pitches and lead terminal numbers. To accommodate these changes, it was necessary that many kinds of constituent parts be prepared and many kinds of processing methods be executed. In particular, regarding the complex bending of the lead terminals 186, as illustrated in FIG. 37, two kinds of initial bending are included (i.e., a case where the lead terminal is bent into the lead terminal 186 indicated in a solid line shown in FIG. 36 and a case where the lead terminal is bent into the lead terminal 186xe2x80x2 indicated in a one-dot chain line shown in the same figure). There are three kinds of subsequent bending, including a first kind corresponding to a state in which the terminal numbers 1, 2 and 3 are arranged in one row in this order, a second kind corresponding to a state in which the terminal number 2 is located on the left side of the terminal numbers 1 and 3, and a third kind corresponding to a state in which the terminal number 2 is located on the right side of the terminal numbers 1 and 3. This is shown in FIG. 37. The second column of permutations in this figure corresponds to the initial bending operation and the third column of permutations in this figure corresponds to the subsequent bending operations. More specifically, the third column represents a view of the components taken from the direction A after completion of all bending steps.
The subsequent bending after the initial bending is three in kind with respect to each of the two kinds of initial bending. Thus, six bending methods become necessary. This made the manufacture and management of these parts complex, which hindered productivity.
The present invention has an object to provide a variable resistor which has a small number of constituent parts and can reduce the kinds of the terminal bending operations required.
To attain the above object, there is provided a variable resistor comprising a first rotor or a second rotor, the first rotor having provided on its surface a resistor and an electrode connected to at least one end portion of the resistor. The second rotor has provided thereon a resistor and electrode at a position obtained by rotating a resistor and electrode symmetrical with those of the first rotor through an angle of 180xc2x0 with respect to the first rotor. The variable resistors further includes at least two slide contactors, and a case provided with a recess portion, whereby either one of the first and second rotors is rotatably accommodated in the recess portion of the case having the slide contactors exposed in a bottom surface thereof. The slide contactors contact the resistor and electrode when the rotor is disposed in the recess. A cover is mounted on an opening of the recess portion of the case.
Here preferably, the resistor provided on each of the first and second rotors is shaped like a horseshoe and the electrode provided on each of the first and second rotors is formed concentrically with the horseshoe resistor. Also, the variable resistor can be of a structure wherein a lead terminal separate from the slide contactor is connected to this slide contactor. Also, the rotors can each be made of insulating resin or ceramic having the resistor and electrode provided on their surface. Further, the rotors can be constructed by combining the substrate having the resistor and electrode provided on their surface and a main body.
Thus, two kinds of rotors are provided, one of which is a first rotor and the other of which is a second rotor having provided thereon a resistor and electrode at a position obtained by rotating a resistor and electrode symmetrically with those of the first rotor through an angle of 180xc2x0 with respect to the first rotor. One of these rotors is selected and then inserted in the case. The terminal number is changed and, as a result, initial bending of the terminal is reduced from the convention two kinds of bending operations to one kind of bending operation.
Also, the cover has mounting claw portions disposed in 180xc2x0 rotation symmetry about a rotation axis of the first and second rotors, and these mounting claw portions are inserted by force into holes provided in the case, whereby the cover is mounted on the case.
The variable resistor can be configured as a sealed structure by mounting the cover onto the opening of the case via an O-ring. Also, by the cover being mounted by a forced insertion method, the conventional sealing operation based on the use of resin becomes unnecessary and in addition the resulting variable resistor requires fewer assembling steps and thus productivity of these devices improves. The forward end portions of the mounting claw portions of the cover are folded back and slits and engagement portions are provided in and on the mounting claw portions. This structure helps prevent the cover from coming off.
Also, the cover has an adjusting opening at its central part and at least one of bending and burring is performed of the edge portion of this adjusting opening toward the side of the rotor. By performing bending or burring of the edge of the adjusting hole provided at the central part of the cover, the insertability of the driver at the adjusting time and the strength of the cover itself is increased. Accordingly, the deformation of the top surface of the cover after the mounting of it is prevented and the contact reliability of the contact between the resistor or electrode and the slide contactor is enhanced.
Further, the variable resistor according to the present invention has an adaptor for maintaining the terminal pitch dimension. By this adaptor, the terminal pitch dimension is maintained stably.